1. Field of the Invention
The present invention relates to a process for preparing 3-dimethylamino-2,2-dimethylpropanal from isobutyraldehyde, formaldehyde and dimethylamine.
2. Discussion of Prior Art
Aminoaldehydes which are derived from the neopentyl structure (i.e. 2,2-dimethylpropyl structure) are of great interest as intermediates for the preparation of pharmaceuticals, plant growth hormones, fungicides, herbicides and flotation auxiliaries. Aminoaldehydes which have a tertiary amino group in the 3-position in addition to the central branching of the carbon chain are of particular importance. These compounds are used, for example, to prepare 3-aminopyridine derivatives, 1,2-dihalopyridazines, benzo-1,3-dioxans, substituted imidazoles and amidines.
It is known to prepare alkyl aminoaldehydes by condensation of CH-acid compounds with formaldehyde and ammonia or amines (Mannich et al in Reports 65, 387 (1932)). This conversion, which can be classified as a special case in the framework of the broad aminomethylation type of reaction, is described as a Mannich reaction.
To form 3-dimethylamino-2,2-dimethylpropanal by the Mannich reaction, one starts from isobutyraldehyde, paraformaldehyde and dimethylamine hydrochloride (Mannich, loc. cit.). An essential feature of this procedure is the presence of an acid, which is added to the reaction medium either as such or in the form of the amine salt. The condensation thus proceeds in an acid medium.
The necessity of operating at pH values below 7 has considerable disadvantages, which lead to serious difficulties in producing the compounds on a technical scale. In addition to the Mannich reaction, a trimerization of isobutyraldehyde to 2,4,6-triisopropyl-1,3,5-trioxane in fact also takes place in acid media, and the yield of the desired aminoaldehyde is considerably reduced. If hydrochloric acid is employed, it is essential to use halogen-resistant reactors.
Moreover, the Mannich base is formed as a salt, from which the aminoaldehyde has to be obtained via a very complicated and costly working-up procedure, which to some extent involves environmentally harmful procedures. The object, therefore, existed of developing a process which avoids the indicated disadvantages and also enables 3-dimethylamino-2,2-dimethylpropanal to be produced in a simple manner on a technical scale.